The argument goes something like this: "I refuse to prove that I exist," says the loch ness monster, "for proof denies faith, and without faith I am nothing." "But," says Man, "the appearances and sightings are a dead giveaway, aren't they? If people see you then you are there. It proves that You exist, and so therefore, by Your own arguments, You don't. QED" "Oh dear," says the loch ness monster, "I hadn't thought of that," and promptly vanishes in a puff of logic."